1. Field of the Invention:
This invention relates to a secondary air supply control system, in which unburnt constituents of exhaust gases from an engine are oxidized with secondary air supplied to an exhaust manifold therein.
2. Description of the Prior Art:
It has been a general practice for a secondary air supply system to interrupt the supply of secondary air to an exhaust manifold for preventing after-firing, during a speed change or engine deceleration.
Meanwhile, it is known that there is no danger of after-firing when secondary air is supplied to an exhaust manifold, when the time required for a speed change is relatively short, or a time during which the engine is maintained in a decelerating condition is relatively short. Thus, there arises a demand for supplying secondary air to an exhaust manifold for oxidizing unburnt emissions in the above cases, thereby preventing the emission of harmful gases to the atmosphere.